1. Field
The subject technology relates generally to electro-absorption modulators (EAMs), and more specifically to methods for optimizing a spur-free dynamic range (SFDR) or a gain in EAMs.
2. Background
An electroabsorption modulator (EAM) is a popular choice for high speed optical modulation due to its small size, high slope efficiency, large modulation bandwidth, and potential for monolithic integration with other optical and electrical components. In order to be compatible with input and output optical fibers, the EAM typically comprises an optical waveguide structure for optical confinement.
The EAM operates via an electric field induced change in the absorption spectrum of an electroabsorption (EA) material of the EAM. In some EAMs, the EA material is an integral part of the optical waveguide. In peripheral coupled waveguide (PCW) EAMs, however, an EA layer comprising the EA material is decoupled from the optical waveguide of the EAM. For example, the EA layer is placed above the waveguide layer and peripheral to an optical waveguide mode, in its evanescent or peripheral field. The low confinement factor in the EA layer (typically below 10%) enhances the optical power handling capability of the EAM by reducing the photogeneratated current. The PCW EAM can have either a lumped electrode configuration or a travelling-wave electrode configuration.
An SFDR and a gain are two important link parameters for evaluating the performance of an EAM. The latter measures the effectiveness of the EAM to transfer the optical input power to the optical output power, while the former measures the ratio of the RMS value of the fundamental response to a next largest noise or harmonic distortion (e.g., intermodulation distortion).